You should know what User-Agent is, and what side effect after it is changed. Please don't complain or report any bug issue about "it the website is broken".

Note: Because Firefox 57 will drop support legacy add-ons, and I don't had any time to migrate it to WebExtensions yet, this project is in maintain mode, bugfix only, no new feature. For Firefox 57+ users, I recommend to use User Agent Switcher instead.